The pair began their evening with dinner at the Bellagio's Prime steakhouse, then rode to the Mirage in Angel's Rolls Royce for the 10:30 p.m. performance of Cirque du Soleil's Beatles tribute LOVE.

The smiling duo walked arm-in-arm into the theater through the main entrance, and throughout the show, a witness tells PEOPLE, "They were snuggling with each other and he was making her laugh. They seemed really happy."

After the final curtain, the pair headed backstage and greeted the cast until just before midnight before leaving through a side door and disappearing into the night in Angel's car.

Diaz and Angel, who has been linked to Minnie Driver, previously met up on Saturday night at the VH1 Rock Honors and later partied at the Jet Nightclub with Diaz's BFF Drew Barrymore. Diaz had been scheduled to leave Las Vegas on Sunday with her friends, sources tell PEOPLE, but decided to extend her stay through Tuesday.

Meanwhile, the actress talked about her relationship with ex-boyfriend Justin Timberlake on an episode of The Ellen DeGeneres Show airing Tuesday. "I love how people just expect when people break up to hate each other," she said, "but you know ... we're still in each other's lives. When you care about somebody, you just want them to be happy and that's what we both are now."

She continued: "Life is amazing. There's nothing not to be happy about."